Receiving system



Oct. 5, 1937. H. F. ELLIOTT RECEIVING SYSTEM Filed June 11, 1952 2 Sheets-Sheet l INVENTOR ffQ/O/a F: EU/Ozz BY HIS ATTORNEY Get. 5, 1937. H. F. ELLIOTT RECEIVING SYSTEM Filed June 11, 1932 2 Sheets-Sheet 2 |NVENT OR Ham/d HEl/z'aff BY H\S ATTORNEY Patented oct. 5.1937

UNITED STATES PATENT -Fri-E "RECEIVING SYSTEM em Elliott, Palo Alto, cane V Application'June 11, 1932, Serial No. 616,586 a V V A .8 Claims. (crest- 20) This invention relates to receiving systems embodying electronic tubesfor amplifying, detecting and controlling signals transmitted by carrier waves and particularly to systems incorporating cation. a

An objectof my invention'is. the provision of methods and means'whereby the functions ofamm plification and detection are accomplished more 1 effectively and more simply than by the methods heretofore available. Another object is'to provide means of detection and amplification whereby the'quality of reproduction is. improved.

matic control of amplification. Another object is to'accomplish thefunc'tions of "rectification,

amplification and automatic control in a single tube, therebyreducing the numberof tubes re-V quired and thereby reducing the size and cost of the equipment needed for radio'reception and. other purposes. 7 Referring 'to the drawings:

ment of elements in specially constructed'tubes which aresuitable for carrying out the objects of my invention. The novel features of these are described and claimed in my cO-pending application, Serial No.'605,186', fi ledfApril l l, 1932.

Fig. 4 shows circuits of a complete broadcast receiver of the tuned 'radio 'frequency type in which the objects of my invention are carriedy out utilizing the tube shown in Fig. 1.

b Fig. 5 shows circuits whereby "the tube of Fig.

1 may be usedin another manner.

Fig.6 shows still another" circuit arrangement,

in this case utilizing tubesof the typeshown in Figs.2and3. I Referring to Fig.1,numera1 l designates a glass envelope for the tube, Numeral 2 designates a cathode Which'may be of the uni-potential type. Numeral 3 designates a connection to the cathode which may be brought out to a terminal on the lines. Numeralsilil and Il designate terminals for the two grids 8 and 9 respectively. Numeral l2 designates an auxiliaryanode placed'around 55 an extended portion of the cathode, and numeral provisions forautomatic-control of the amplifi Another object is to 'extend theran ge'of autoconnected directly totne cathodewithin the tube [3 shows an external terminal connection for the auxiliary anode. I

Fig. 2 shows a second specially constructed tube, also suitable for carrying out the objects of the invention. 'Ihis tube'is similarto that of Fig. 1 except that an additional electrode in the form of a screen grid [4 is placed between the control grids 89 and the main anode 6. A connection for thescreen is shown at l5.

Fig. 3 shows a third specially constructed tube likewise suitable for carryingfout the objects of the invention. This tube is *similar to that of Fig. 2 except that-an additionalscreen-electrode I6 is added between the screen grid l4 and the anode 6. This added screen, l5, may serve as a 5 suppressor grid to minimize the effects of secondary emissionas is'nowwellunderstood in connectionwiththeso called pentodef tubes now in commercial use. The suppressor grid may be or. a connection Il' maybe brought out to an ex- 7 *ternal terminal. Figs. 1, 2 and 3 show in outline the 'arrang'e- Referring to Fig.4, numerals and I9 desig-" nate amplifier tubes which serve to amplify the incoming signals Numeral designates adetector tube, and numeral 2;! an audio amplifier or power output tube. Tube 22 is a rectifier which, together with the filter comprising capacitors 23, 24 and 25 and reactors 2t and Z'i, serve to supply direct current potentials of a few hundred volts for the operation of the receiver. Inasmuchas the functions and the connections of all of the tubes, except the detector are close ly in accordance with standard practice in commercial broadcast receivers now in wide; use,' only the connections and functions of tube 20 will be described in detail. The elements of tube 20" should preferably be; arranged substantially in accordance with Fig. 1 or 2, to which reference has already been made. 7 in Fig. 1 is used, then the screen grid I4, resistor 28 and by-pass capacitor 29 maybe omitted from the circuit shown in Fig. 4, otherwise the description which follows is applicable to both the tube of Fig. 1 and the tube oflFig. 2. The principal difference'between the two is that the use of the a screen enables the tube of Fig. 2 to give somewhat higher audio amplification than the tube of a Fig. l' which is sometimes advantageous when very high sensitivity is desired; v a

In Fig. 4 the amplified signals delivered by tube [9 areapplied to the twogrids 8' and 9 of tube' 29 in phase opposition. This is accomplished 'byarranging the circuit which interlinks the two tubes l9 and 20 so that point 34, in this interlink- If the structure shown ing circuit, is substantially at ground potential insofar as the radio frequency currents circulating in this circuit are concerned. This condition arises from the fact that point 34 is a potential nodal point in the interlinking circuit which comprises two resonant circuits 30-3l, and 32- 3, which are connected in series in so far as radio frequency currents are concerned. Circuit 303l is tuned to the frequency to be received, as is also circuit 32--33. The circuits are joined in series at point 34, which is thus a potential nodal point for radio frequency currents and is above ground potential only by the amount of the in-phase potential required to make up the energy losses associated with circuit 3233. It will be noted that point 34 is not grounded, but

is isolated from ground by resistor 31 having several hundred thousand ohms resistance as outlined below. Thus it will be seen that point 34 is not grounded, but being a nodal point, is actually at substantially ground potential. Radio frequency currents in the interlinking circuit flow in series through capacitor 3|, inductor 30, inductor 32 and capacitor 33. It will be noted that the two tuning capacitors 3| and 33, of this interlinking circuit, each has one of its electrodes grounded. This makes it possible to construct these two capacitors, together with capacitors 3E and 36 which tune the input circuits of tubes l8 and I9, as a single unit with common rotor, in accordance with standard practice in broadcast receivers. The two grids 8 and 9 of tube 20 are shown as connected to taps on coils 30 and 32. The locations of these taps should preferably be chosen so that the potentials applied to grids 8 and 9 are substantially equal and opposite in phase, and of a value which gives maximum response from tube 20 without imposing too heavy a load upon the circuits to which the grids are connected. In the arrangement shown in Fig. 4, the cathode 2 of tube 20 is grounded and point 34 in the interlinking circuit is connected to ground and thence to the cathode through load resistor 31, sometimes called a grid leak. Resistor 31, which is preferably of the order of a few hundred thousand ohms, may be shunted by the capacitor 38, of the order of 50 to 100 micro-microfarads. Alternately capacitor 36 may be omitted if the stray capacitances of the system are sufiicient to maintain balanced input potentials for grids 8 and 9.

In operation the two grids 8 and 9, together with the cathode 2, act as a full wave rectifier for the radio frequency potentials which are applied to the two grids. The process of rectification results in a pulsating direct current across resistor 31. These pulsations correspond to the modulations of the incoming signals and are applied to the two grids 8 and 9 in parallel. Tube 20 therefore acts as an audio-frequency amplifier for the rectified signals. The amplified output of tube 20 may be applied directly to a translating device or further amplified in tube 2!, as shown in Fig. 4. Any suitable form of coupling arrangement may be used between tube 26 and tube 2| in Fig. 4 resistance-capacitance coupling is shown. Resistor 33 is preferably of the order of 100,000 ohms; capacitor 40 of the order of .05 microfarad; resistor 4! is preferably a potentiometer having a total resistance of about megohm and serves to control the input to tube 7-! I, and consequently the output from speaker following the latter.

The negative potentials which accumulate on the grids 8 and 9 during the process of rectification appear at point 34 and may be used automatically to control the amplification in tubes I8 and I 9. The automatic volume control circuits through which this is carried out are shown in Fig. 4 as comprising resistors 42, 45 and 41, together with by-pass capacitors 43, 46 and 48. The resistors may be of the order of to 2 megohms and the by-pass capacitors of the order of .05 to .1 microfarad. Since this arrangement is in accordance with commercial practice in broadcast receivers having automatic volume control, further details are unnecessary here.

In cases where it is desired to maintain a very close balance in the potentials applied to grids 8 and 9 of tube 20, capacitor 64 and inductor 65 may be connected as shown to balance the effect of capacitor 66 and inductor 61. Inductor 65 may be shunted by a network simulating the effect of tube I9 on inductor 61 if desired.

Referring now to Fig. 5, circuits are shown whereby the range of the automatic volume control system may be extended, and also whereby the governing action of the automatic control maybe caused to take effect when the signals reach a predetermined level. With this arrangement, signals below this level are not affected by the automatic control and there is, consequently, no attenuation of weak signals. The circuits of Fig. are similar to those of Fig. 4 except that the load resistor 31 is connected directly between point 34 and cathode 2, and the latter instead of being grounded is connected through resistors 49 -50 to a point in the power supply system which is negative with respect to ground. This negative potential should preferably be of the order of 100 volts and may, if convenient, be, obtained by connecting point 56 to the negative side of the speaker field. Capacitors 5|, 52 and 53 serve to prevent pulsations in the power supply system from circulating in thecircuits of tube 20. In the circuits shown in Fig. 5, the plate circuit of tube 20 is shown as including an auto-transformer 54, the output of which may be coupled to a succeeding tube by means of coupling capacitor 40 and potentiometer 4|, as in Fig. 4. Alternately a standard transformer or resistance coupling may be used in place of the auto-transformer. In order to obtain the full benefit of the connections of Fig. 5, the positive potential applied to point 55 and the negative potential applied to point 56 should be adjusted so that, in the absence of signals, cathode 2 is positive with respect to ground by a potential of to 30 volts. When signals are received, the space current in tube is reduced and the drop across resistors 49 and 50 is consequently reduced. Cathode 2 then more nearly approaches the negative potential of point 56. When signals of sufiicient strength are received to cause cathode 2 to become negative with respect to ground, electrons will be attracted from the cathode to the auxiliary anode l2, thereby causing current to flow through resistor 51 and causing point 58 to become negative with respect to ground. This negative potential at point 58 may be used for automatic volume control by connecting point 58 to the grid circuits of the preceding tubes, as through resistor 42, by-pass capacitor 43 and bus 44, which may be arranged as shown in Fig. 4.

Another arrangement whereby tubes of the type shown in the Figs. 1, 2 and 3 may be used to perform the functions of rectification, audio amplification and automatic volume control is shown in Fig. 6. In this arrangement the auxiliary anode l2, together with the cathode 2,

serve as a half wave rectifier whereby the ampli-' i resistor 59,by-pass capacitors 60 and GI and po tentiometer 62. The direct current component 10 of the potentials across resistor 3'! may be ap plied for automatic volume control by connecting resistor 42 and capacitor 43 to point 63 and connecting the grid circuits of the amplifier tubes to bus M, as in Fig. 4. Biasing potentials for the 15 grids 8 and 9 may be applied to potentiometer E2 in the same manner as is shown for potentiometer t! in Fig. l, or, alternatively, the bias obtained fromrthe rectified signals as is the case for tube 20 in Figures 4 and 5. 20 If amplifier tubes of the present multi-mu tivity of the receiver may be controlled by adjusting the potentials applied to the electrodes of these tubes in any of the customary ways, as by the potentiometer 68, 69, 10 shown in Fig. 4. This feature may conveniently be retained for adjusting the amount of gain preceding the de-' tector and consequently the extent to which the receiver will respond to incoming signals and atmospheric disturbances.

While the circuits shown herein have all been directed especiallyto tuned radio frequency receivers havingone side of the tuning condensers grounded, it will be evident to those familiar with 35 radio receivers that the circuits may also be applied to instruments of the superheterodyne type, and that many variations in circuit arrangements and tube construction are possible. My invention is not limited to the arrangement shown, 40 but is best defined in the appended claims.

What I claim is: t 1. Amplifying and detecting apparatus embodying two discrete resonant circuits connected in series with tuning capacitors having two electrodes 45 maintained at a common potential, an electron tube having a cathode and two grids symmetrically placed in the electron stream and having, equal effect thereon, connectionsto the two grids from points of equaland opposite potentials in 50 said resonant circuits, a connection includ ingan impedance from an electrical center point in the circuits to said cathode and a connection I including an impedance from said center to gain control means in the amplifier.

55 2. Signal amplifying and detecting apparatus embodying resonant circuitswith tuning capacitors having a plurality of electrodes maintained at a common potential, an electron tube having a cathode and two grids symmetrically located in the electron stream and having equal effect thereon, an input circuit for the tube comprising an inductor tuned by two of the'capacitors in series, connections from the grids to points on the inductor whereby equal signal potentials may be applied to the two grids in phase opposition, connections including animpedance from the electrical center of the inductor to' said cathode,

and means whereby rectified signal potentials associated with the impedance may be utilized 7 for automatic control of amplification.

3. Carrier wave amplifying and detecting apparatus comprising .an amplifier and a detector having resonant circuits with a plurality of tun-f ing capacitors one side ofeach of which is type are employed at l8 and I9, Fig. 4, the sensigrounded, an electron tube having a cathode, an anodegand two grids symmetrically located in the electron stream and having equal efiect thereon, an electrically symmetrical input circuit comprising two of the tuning capacitors with an inductor and the two grids, connections including an impedance from the electrical center of the inductor to the cathode, and the connections in-.

cluding an impedance from said center to control means in the amplifying apparatus.

'4. A carrier wave amplifier and detector comprising .a plurality of tuning capacitors one side of each of which is grounded, an electron tube having a cathode, an anode, two grids symmetrically located in the electron stream and having equal effect thereon, and an auxiliary anode, an electrically symmetrical input circuit comprising two of the tuning capacitors with an inductor as well as thetwo grids and an impedance in a circuit between the grids and cathode, an output circuit comprising the cathode, anode, an in1- pedance and a source of potential, and a volume control circuitincluding the source of potential, the cathode, the auxiliary anode and control means in the amplifier whereby said tube serves to rectify and amplify signals applied thereto, and to control the amplification of preceding tubes respecting signals above a predetermined level metrical resonant circuits, and a carrier wave nodal point intermediate of said resonant cir- Within the detector, and deriving potentials for automatic control'from said carrier wave nodal point. a

7. The method of carrier wave detection and automatic gain control in a radio circuit having a carrier wave input; detector, two electrically symmetrical resonant circuits, and a carrier wave nodal point between said two resonant circuits; which comprises balancing the carrier wave input to the detector in the two said resonant circuits,

. balancing the reaction of the carrier wave within the detector, and deriving potentials for automatic control from'said carrier wave nodal point.

8- Themethod of carrier wave detection and automatic gain control in a radio circuit having a carrier wave input, detector, electrically symmetrical resonant circuits, and a carrier wave nodal point intermediate of said resonant circuits; which comprises introducing the carrier wave in series through the resonant circuits, balancing the carrier' waveinput to the detector in the resonant circuits, balancing the reaction of the carrier wavewithin the detector, and establishing a nodal point automatic control potential.

' HAROLD F. ELLIOTT. 

